Friday, March 9, 2012

Encapsulation in Java or object oriented programming
language is a concept which enforce protecting variables, functions from outside
of class, in order to better manage that piece of code and having least impact
or no impact on other parts of program duec to change in protected code. Encapsulation in Java is visible at
different places and Java language itself provide many construct to encapsulate
members. You can completely encapsulate a member be it a variable or method in
Java by using private keyword and you can even achieve a
lesser degree of encapsulation in Java by using other access modifier like protected or public. true value of encapsulation is realized in an environment
which is prone to change a lot and we know that in software requirements
changes every day at that time if you have your code well encapsulated you can
better manage risk with change in requirement. Along with abstaction
in java and polymorphism
in Java, Encapsulation is a must know concept. In this java tutorial we will see How to use encapsulation in Java, advantage and disadvantage of Encapsulation
and various design patterns and real life problems which makes use of
Encapsulation object oriented concept. If you are
looking for a quick guide on both OOPS and SOLID design principle in Java than
you may find 10
Object Oriented Design principles Java programmer should knowinteresting.

What is Encapsulation in Java

Encapsulation is nothing but protecting anything
which is prone to change. rational behind encapsulation is that if any
functionality which is well encapsulated in code i.e maintained in just one
place and not scattered around code is easy to change. this can be better explained
with a simple example of encapsulation in Java. we all know that constructor is
used to create object in Java and constructor can accept argument. Suppose we
have a class Loan has a constructor and than in various
classes you have created instance of loan by using this constructor. now
requirements change and you need to include age of borrower as well while
taking loan. Since this code is not well encapsulated i.e. not confined in one
place you need to change everywhere you are calling this constructor i.e. for
one change you need to modify several file instead of just one file which is
more error prone and tedious, though it can be done with refactoring feature of
advanced IDE wouldn't it be better if you only need to make change at one place
? Yes that is possible if we encapsulate Loan creation logic in one method say createLoan() and client code call this method and
this method internally crate Loan
object. in this case you only need to modify this method instead of all client code.

publicLoan createLoan(StringloanType){ //processing based on loan type and than returning loan object

returnloan;

}

}

In this same
example of Encapsulation in Java you
see all member variables are made private so they are well encapsulated you can
only change or access this variable directly inside this class. if you want to
allow outside world to access these variables is better creating a getter and
setter e.g. getLoan() that allows you to do any kind of validation, security
check before return loan so it gives you complete control of whatever you want
to do and single channel of access for client which is controlled and managed.

Advantage of Encapsulation in Java and OOPS

Here are few
advantages of using Encapsulation
while writing code in Java or any Object
oriented programming language:

1.
Encapsulated Code is more flexible and easy to change with new requirements.

2.
Encapsulation in Java makes unit testing easy.

3.
Encapsulation in Java allows you to control who can access what.

4.
Encapsulation also helps to write immutable class in Java which are a good
choice in multi-threading

environment.

5.
Encapsulation reduce coupling of modules and increase cohesion inside a module
because all piece of one thing

are
encapsulated in one place.

6.
Encapsulation allows you to change one part of code without affecting other
part of code.

What should you encapsulate in code

Anything which can be change and more likely to change in near future is candidate of
Encapsulation. This also helps to write more specific and cohesive code. Example
of this is object creation code, code which can be improved in future like
sorting and searching logic.

Design Pattern based on Encapsulation in
Java

Many design
pattern in Java uses encapsulation concept, one of them is Factory
pattern which is used to create objects. Factory pattern is better choice
than new operator for creating object of those classes whose creation logic can
vary and also for creating different implementation of same interface. BorderFactory class of JDK is a good example of
encapsulation in Java which creates different types of Border and encapsulate creation logic of Border. Singleton
pattern in Java also encapsulate how you create instance by providing getInstance() method. since object

is created
inside one class and not from any other place in code you can easily change how
you create object without

affect other
part of code.

Important
points aboue encapsulation in Java.

1.
"Whatever changes encapsulate it" is a famous design principle.

2.
Encapsulation helps in loose coupling and high cohesion of code.

3. Encapsulation in Java is achieved using access modifier private, protected and public.

4. Factory
pattern , Singleton pattern in Java makes good use of Encapsulation.

Does Data hiding and Encapsulation is same principle ? Some one ask me in OOPS Interview that What is data hiding and What is Encapsulation, I am getting confused is it two different concept or just one ?

@Anonymous, you are correct. Actually createLoan() was that static factory method which supposed to return Loan object, until now, when I realized it's missing static modifier :). Thanks for pointing it out.

Hello,I am unable to get the differences between Object initialization through Parameterized constructor and the creatLoan() method from the explanation above. Both are doing the same job..

Suppose, If we want to add a new attribute to the class in future (borrower age as per the example), Its necessary to modify all the object creation codes in all the files. But how come this effort will be reduced in case of the creator methods?? (Because we are introducing an extra attribute in the class, we need it through some mechanism from the users(object creation requestor files). And that will ofcourse require extra modifications in files.,

Gone through above loan creation example. My question is do we need to pass relevant parameters to createLoan method

ex : createLoan(int duration, String loan, String borrower, String salary) . if we not providing above parameter how can we create loan object dynamically. Then how can code flexibility happen, everywhere in application where createLoan method has no change ?